Rattly noise when cold starting

[cpk]

Hi All,

My 07 GS450H has recently developed a noisy/rattly engine on startup for the first few seconds of start when starting from cold.  It's as if the oil hasn't yet got to those parts yet making the noise, it soon goes and then purrs.  Oil level is fine.

 

Any ideas, timing chain? Tappets?  Is this common on a car with 120k miles?

[OldTrout]

Chris,

If this is the oil a bit slow getting to the VVT mechanism, Britprius is going to do a writeup on curing this.

John

[Britprius]

The noise is cased by the oil draining down from the VVT "variable valve timing" sprockets. They then rattle on cold start till they are filled with oil. According to Lexus this is not problematic apart from the noise. The official Lexus cure for this is to strip the top of the engine, and replace the 4 VVT sprockets, and empty your wallet. Many Toyota/Lexus engines suffer with this problem to varying degrees.

I have developed a low cost reliable solution that pressurises the oil system before the engine starts eliminating the noise. The system also reduces cold start engine ware as the engine is lubricated before it turns over to start.

I am testing the system at the moment to iron out any possible bugs, but I am virtually at the point of issuing the details of the method here on LOC. 

Parts used are all obtainable on the net the most expensive part being a 12volt DC solenoid valve at circa £12. The other parts are mainly small pipe fittings, flexible hose, and a suitable pressure container holding about 1ltr.

John.

[cpk]

Thanks for the responses.  Your solution sounds like a cracking piece of engineering!

What causes it to just suddenly start happening?  It might have starting making noises since it's last service but I wouldn't put money on it.

 

It's still under warranty, I'd assume from your response that lexus think it's not a problem so they won't address it?

[noby76]

19 hours ago, cpk said:

 It's as if the oil hasn't yet got to those parts yet making the noise, it soon goes and then purrs.  Oil level is fine.

some engine Oil's have been engineered to stick or have a thin layer coating on critical parts of the engine which aids in cold start lubrication as those parts will be pre-lubed prior to starting the engine.. I know Castrol Magnatec 5W-30 full Syn has such formulation in their oils.. worth giving this a try before you start emptying your wallet on VVTi Sprockets..

[Farqui]

Chris @cpk, the VVT oil feeds to the heads have filters in them (1 per bank of the v6) and these may have become clogged over time.  I spoke to a Lexus tech recently who said that provided regular oil changes had occurred then the filters were unlikely to have clogged up.  They're both easily accessible and I may well check mine as some point.

Or as John mentions, the oil may have been changed during the last service which has affected the lubed parts and/or drain back rate.

[Britprius]

As mentioned in previous posts these filters in the line to the cams "can become partially blocked, and are certainly worth checking. This however is not the prime reason for the noise as if the oil were returning back through the filters to drain the sprockets this would increase the time taken for the oil to drain back. They would however increase the time taken to refill the empty sprockets, and increase the duration of the noise.

On belt driven versions of the engines an "O" ring seal lets the oil escape as the seal wares, and hardens producing an external oil leak at the sprockets, and is visible behind the belt driven sprockets.

The GS450H engine is chain driven so that the sprockets are enclosed within the crank case so any leak back returns to the sump with no sign of any external oil leak.

In the US there is a recall for this, but not for the hybrid versions of the engine where modified sprockets are fitted. I do not know if the recall applies in the UK.
The none hybrid cars with normal starter motors have been know to loosen the bolts that holds the sprockets to the cams. The bolts falling into the timing chain with disastrous results. However because the starting method in the hybrid is faster, and smoother Lexus say it does not happen with the hybrids. Again however there has been a reported incidence of this here on LOC that I believe Lexus would not acknowledge.

It is difficult to know how different oils may affect the situation. More viscous oils (10w40 or 10w50) may take longer to drain back, but they will also be slower at refilling the system. Thinner oils (0w20 or 5w30) may drain back faster, but will also refill the system faster. The OEM specified oil for the MK3 GS450H is 5w30. I now use 0w20 without any noticeable difference in noise level or duration until the pre-lube system was fitted eliminating the noise completely.

There is within the sprockets a spring loaded locking pin that looks like it should lock the sprocket to the cam when the engine stops. When oil pressure reaches a given level the locking pin is released by the oil pressure. It may be that the return spring behind the pin breaks or becomes weak or the pin sticks in it's bore. In either case the sprocket would then not lock as the oil drains away. It may be that this is the mechanism that has been modified. 

The job of the pin can only be to stop the noise until oil has filled the sprockets at pressure, and this is what my system does by pressurising the system before the sprockets move.

There are many video's on the tube showing the pin "search Toyota VVT", but know explanation of it's purpose.  

John.